Re: [Patch mptcp-net 1/3] mptcp: add backlog_list bug reproducer test

[gang.yan@linux.dev]

>February 5, 2026 at 5:20 PM, "Paolo Abeni" <pabeni@redhat.com mailto:pabeni@redhat.com?to=%22Paolo%20Abeni%22%20%3Cpabeni%40redhat.com%3E > wrote:
Hi, Paolo:

Thanks for your detailed review comments.

This patch is for temporary testing purposes only to reproduce the
backlog_list-related issues, and it's not meant for merging. In the upcoming
v2 version, I'll incorporate all your suggestions and add the appropriate
"do-not-merge" tag.

Best regards,
Gang

> 
> On 2/5/26 7:41 AM, Gang Yan wrote:
> 
> > 
> > From: Gang Yan <yangang@kylinos.cn>
> >  
> >  This patch introduces a test program to reproduce bugs related to the
> >  backlog_list in MPTCP. The test is derived from tls.c in the selftests
> >  suite, but adapted to work without TLS configuration specifically for
> >  MPTCP testing.
> >  
> >  The program performs chunked sendfile operations with various payload
> >  sizes to exercise different code paths and trigger backlog_list-related
> >  issues.
> >  
> >  It can be run in .virtme-exec-run:
> >  run_loop run_selftest_one ./multi_chunk.sh
> >  
> >  '''
> >  selftest Test: ./multi_chunk.sh
> >  TAP version 13
> >  1..1
> >  [stalls for a while]
> >  ^C
> >  
> >  '''
> >  
> >  Co-developed-by: Geliang Tang <tanggeliang@kylinos.cn>
> >  Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
> >  Signed-off-by: Gang Yan <yangang@kylinos.cn>
> >  ---
> >  tools/testing/selftests/net/mptcp/Makefile | 1 +
> >  .../testing/selftests/net/mptcp/multi_chunk.c | 148 ++++++++++++++++++
> >  .../selftests/net/mptcp/multi_chunk.sh | 37 +++++
> >  3 files changed, 186 insertions(+)
> >  create mode 100644 tools/testing/selftests/net/mptcp/multi_chunk.c
> >  create mode 100755 tools/testing/selftests/net/mptcp/multi_chunk.sh
> >  
> >  diff --git a/tools/testing/selftests/net/mptcp/Makefile b/tools/testing/selftests/net/mptcp/Makefile
> >  index 22ba0da2adb8..087e6ae6f0b8 100644
> >  --- a/tools/testing/selftests/net/mptcp/Makefile
> >  +++ b/tools/testing/selftests/net/mptcp/Makefile
> >  @@ -24,6 +24,7 @@ TEST_GEN_FILES := \
> >  mptcp_diag \
> >  mptcp_inq \
> >  mptcp_sockopt \
> >  + multi_chunk \
> >  pm_nl_ctl \
> >  # end of TEST_GEN_FILES
> >  
> >  diff --git a/tools/testing/selftests/net/mptcp/multi_chunk.c b/tools/testing/selftests/net/mptcp/multi_chunk.c
> >  new file mode 100644
> >  index 000000000000..8c97db58a6db
> >  --- /dev/null
> >  +++ b/tools/testing/selftests/net/mptcp/multi_chunk.c
> >  @@ -0,0 +1,148 @@
> >  +#define _GNU_SOURCE
> >  +#include <stdio.h>
> >  +#include <stdlib.h>
> >  +#include <string.h>
> >  +#include <unistd.h>
> >  +#include <fcntl.h>
> >  +#include <sys/socket.h>
> >  +#include <netinet/in.h>
> >  +#include <sys/sendfile.h>
> >  +#include <sys/types.h>
> >  +#include <sys/stat.h>
> >  +#include <errno.h>
> >  +#include <arpa/inet.h>
> >  +#include <sys/wait.h>
> >  +
> >  +#ifndef IPPROTO_MPTCP
> >  +#define IPPROTO_MPTCP 262
> >  +#endif
> > 
> Minor nit: I think we can avoid the compiler guards here; older test
> program have them for historical reasons.
> 
> > 
> > +
> >  +#define TLS_PAYLOAD_MAX_LEN 16384
> > 
> Possibly this macro should be renamed, i.e. to PAYLOAD_MAX_LEN and
> likely the value increased to 64K
> 
> > 
> > +#define TEST_PORT 12345
> >  +
> >  +static void chunked_sendfile(int cfd, int sfd,
> >  + size_t chunk_size,
> >  + size_t extra_payload_size)
> >  +{
> >  + char buf[TLS_PAYLOAD_MAX_LEN];
> >  + uint16_t test_payload_size;
> >  + size_t recved = 0;
> >  + size_t sent = 0;
> >  + int size = 0;
> >  + int ret;
> >  + char filename[] = "/tmp/mytemp.XXXXXX";
> >  + int fd = mkstemp(filename);
> >  + off_t offset = 0;
> >  +
> >  + unlink(filename);
> >  + if (fd <= 0) {
> >  + perror("tempfile");
> >  + exit(1);
> > 
> Here and below you could use the error() libcall instead of the
> perror/exit combo.
> 
> > 
> > + }
> >  + if (chunk_size < 1) {
> >  + perror("chunksize");
> >  + exit(1);
> >  + }
> >  +
> >  + test_payload_size = chunk_size + extra_payload_size;
> >  + if (test_payload_size > TLS_PAYLOAD_MAX_LEN) {
> >  + perror("payload_size");
> >  + exit(1);
> >  + }
> >  + memset(buf, 1, test_payload_size);
> >  + size = write(fd, buf, test_payload_size);
> >  + if (size != test_payload_size) {
> >  + perror("file write");
> >  + exit(1);
> >  + }
> >  + fsync(fd);
> >  +
> >  + while (size > 0) {
> >  + ret = sendfile(sfd, fd, &offset, chunk_size);
> >  + if (ret <= 0)
> >  + exit(1);
> >  + size -= ret;
> >  + sent += ret;
> >  + }
> >  + printf("[client] sent %zu bytes\n", sent);
> >  +
> >  + recved = recv(cfd, buf, test_payload_size, MSG_WAITALL);
> >  + printf("[server] receieved %zu bytes\n", recved);
> > 
> Possibly the above 2 print should be off by default and enabled via
> command line switch.
> 
> > 
> > +
> >  + if (recved != test_payload_size)
> >  + exit(1);
> >  +
> >  + close(fd);
> >  +}
> >  +
> >  +int main()
> >  +{
> >  + int sfd = socket(AF_INET, SOCK_STREAM, IPPROTO_MPTCP);
> >  + int cfd = socket(AF_INET, SOCK_STREAM, IPPROTO_MPTCP);
> >  + struct sockaddr_in addr = {0};
> >  + socklen_t addrlen = sizeof(addr);
> >  +
> >  + printf("==== multi_chunk_sendfile MPTCP test ====\n");
> >  +
> >  + if (sfd < 0 || cfd < 0) {
> >  + perror("socket");
> >  + exit(1);
> >  + }
> >  +
> >  + addr.sin_family = AF_INET;
> >  + addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
> >  + addr.sin_port = htons(TEST_PORT);
> >  +
> >  + if (bind(sfd, (struct sockaddr *)&addr, sizeof(addr)) < 0) {
> >  + perror("bind");
> >  + exit(1);
> >  + }
> >  +
> >  + if (listen(sfd, 1) < 0) {
> >  + perror("listen");
> >  + exit(1);
> >  + }
> >  +
> >  + if (getsockname(sfd, (struct sockaddr *)&addr, &addrlen) < 0) {
> >  + perror("getsockname");
> >  + exit(1);
> >  + }
> >  +
> >  + if (connect(cfd, (struct sockaddr *)&addr, sizeof(addr)) < 0) {
> >  + perror("connect");
> >  + exit(1);
> >  + }
> >  +
> >  + int nfd = accept(sfd, NULL, NULL);
> >  + if (nfd < 0) {
> >  + perror("accept");
> >  + exit(1);
> >  + }
> >  +
> >  + chunked_sendfile(cfd, nfd, 4096, 4096);
> >  + chunked_sendfile(cfd, nfd, 4096, 0);
> >  + chunked_sendfile(cfd, nfd, 4096, 1);
> >  + chunked_sendfile(cfd, nfd, 4096, 2048);
> >  + chunked_sendfile(cfd, nfd, 8192, 2048);
> >  + chunked_sendfile(cfd, nfd, 4096, 8192);
> >  + chunked_sendfile(cfd, nfd, 8192, 4096);
> >  + chunked_sendfile(cfd, nfd, 12288, 1024);
> >  + chunked_sendfile(cfd, nfd, 12288, 2000);
> >  + chunked_sendfile(cfd, nfd, 15360, 100);
> >  + chunked_sendfile(cfd, nfd, 15360, 300);
> >  + chunked_sendfile(cfd, nfd, 1, 4096);
> >  + chunked_sendfile(cfd, nfd, 2048, 4096);
> >  + chunked_sendfile(cfd, nfd, 2048, 8192);
> >  + chunked_sendfile(cfd, nfd, 4096, 8192);
> >  + chunked_sendfile(cfd, nfd, 1024, 12288);
> >  + chunked_sendfile(cfd, nfd, 2000, 12288);
> >  + chunked_sendfile(cfd, nfd, 100, 15360);
> >  + chunked_sendfile(cfd, nfd, 300, 15360);
> >  +
> >  + close(cfd);
> >  + close(nfd);
> >  + close(sfd);
> >  +
> >  + printf("==== test ends ====\n");
> >  + return 0;
> >  +}
> >  diff --git a/tools/testing/selftests/net/mptcp/multi_chunk.sh b/tools/testing/selftests/net/mptcp/multi_chunk.sh
> >  new file mode 100755
> >  index 000000000000..c0352c89087f
> >  --- /dev/null
> >  +++ b/tools/testing/selftests/net/mptcp/multi_chunk.sh
> >  @@ -0,0 +1,37 @@
> >  +#!/bin/bash
> >  +# SPDX-License-Identifier: GPL-2.0
> >  +
> >  +. "$(dirname "${0}")/mptcp_lib.sh"
> >  +
> >  +cleanup()
> >  +{
> >  + if [ -n "$pid" ] && kill -0 "$pid" 2>/dev/null; then
> >  + kill "$pid" 2>/dev/null
> >  + wait "$pid" 2>/dev/null
> >  + fi
> >  +
> >  + mptcp_lib_ns_exit "${ns1}"
> >  +}
> >  +
> >  +init()
> >  +{
> >  + mptcp_lib_ns_init ns1
> >  +
> >  + local i
> >  + for i in $(seq 1 4); do
> >  + mptcp_lib_pm_nl_add_endpoint "${ns1}" "127.0.0.1" flags signal port 1000$i
> >  + done
> >  +
> >  + mptcp_lib_pm_nl_set_limits "${ns1}" 8 8
> >  +
> >  + ip netns exec ${ns1} ip mptcp endpoint show
> >  + ip netns exec ${ns1} ip mptcp limits
> >  +}
> >  +
> >  +init
> >  +trap cleanup EXIT
> >  +
> >  +ip netns exec $ns1 ./multi_chunk &
> >  +
> >  +pid=$!
> >  +wait $pid
> > 
> I think it would be nice to emit an ok/fail message as other tests
> 
> /P
>